Ansible works against multiple systems in your infrastructure at the same time.
It does this by selecting portions of systems listed in Ansible’s inventory,
which defaults to being saved in the location /etc/ansible/hosts.
You can specify a different inventory file using the -i<path> option on the command line.

Not only is this inventory configurable, but you can also use multiple inventory files at the same time and
pull inventory from dynamic or cloud sources or different formats (YAML, ini, etc), as described in Working With Dynamic Inventory.
Introduced in version 2.4, Ansible has inventory plugins to make this flexible and customizable.

The inventory file can be in one of many formats, depending on the inventory plugins you have.
For this example, the format for /etc/ansible/hosts is an INI-like (one of Ansible’s defaults) and looks like this:

It is ok to put systems in more than one group, for instance a server could be both a webserver and a dbserver.
If you do, note that variables will come from all of the groups they are a member of. Variable precedence is detailed in a later chapter.

If you have hosts that run on non-standard SSH ports you can put the port number after the hostname with a colon.
Ports listed in your SSH config file won’t be used with the paramiko connection but will be used with the openssh connection.

To make things explicit, it is suggested that you set them if things are not running on the default port:

badwolf.example.com:5309

Suppose you have just static IPs and want to set up some aliases that live in your host file, or you are connecting through tunnels.
You can also describe hosts via variables:

In INI:

jumper ansible_port=5555 ansible_host=192.0.2.50

In YAML:

...hosts:jumper:ansible_port:5555ansible_host:192.0.2.50

In the above example, trying to ansible against the host alias “jumper” (which may not even be a real hostname) will contact 192.0.2.50 on port 5555.
Note that this is using a feature of the inventory file to define some special variables.
Generally speaking, this is not the best way to define variables that describe your system policy, but we’ll share suggestions on doing this later.

Note

Values passed in the INI format using the key=value syntax are not interpreted as Python literal structure
(strings, numbers, tuples, lists, dicts, booleans, None), but as a string. For example var=FALSE would create a string equal to ‘FALSE’.
Do not rely on types set during definition, always make sure you specify type with a filter when needed when consuming the variable.

If you are adding a lot of hosts following similar patterns, you can do this rather than listing each hostname:

[webservers]www[01:50].example.com

For numeric patterns, leading zeros can be included or removed, as desired. Ranges are inclusive. You can also define alphabetic ranges:

Be aware that this is only a convenient way to apply variables to multiple hosts at once; even though you can target hosts by group, variables are always flattened to the host level before a play is executed.

There are two default groups: all and ungrouped. all contains every host.
ungrouped contains all hosts that don’t have another group aside from all.
Every host will always belong to at least 2 groups.
Though all and ungrouped are always present, they can be implicit and not appear in group listings like group_names.

The preferred practice in Ansible is to not store variables in the main inventory file.

In addition to storing variables directly in the inventory file, host and group variables can be stored in individual files relative to the inventory file (not directory, it is always the file).

These variable files are in YAML format. Valid file extensions include ‘.yml’, ‘.yaml’, ‘.json’, or no file extension.
See YAML Syntax if you are new to YAML.

Assuming the inventory file path is:

/etc/ansible/hosts

If the host is named ‘foosball’, and in groups ‘raleigh’ and ‘webservers’, variables
in YAML files at the following locations will be made available to the host:

/etc/ansible/group_vars/raleigh# can optionally end in '.yml', '.yaml', or '.json'/etc/ansible/group_vars/webservers/etc/ansible/host_vars/foosball

For instance, suppose you have hosts grouped by datacenter, and each datacenter
uses some different servers. The data in the groupfile ‘/etc/ansible/group_vars/raleigh’ for
the ‘raleigh’ group might look like:

---ntp_server:acme.example.orgdatabase_server:storage.example.org

It is okay if these files do not exist, as this is an optional feature.

As an advanced use case, you can create directories named after your groups or hosts, and
Ansible will read all the files in these directories in lexicographical order. An example with the ‘raleigh’ group:

All hosts that are in the ‘raleigh’ group will have the variables defined in these files
available to them. This can be very useful to keep your variables organized when a single
file starts to be too big, or when you want to use Ansible Vault on a part of a group’s
variables.

Tip: The group_vars/ and host_vars/ directories can exist in
the playbook directory OR the inventory directory. If both paths exist, variables in the playbook
directory will override variables set in the inventory directory.

Tip: Keeping your inventory file and variables in a git repo (or other version control)
is an excellent way to track changes to your inventory and host variables.

By default variables are merged/flattened to the specific host before a play is run. This keeps Ansible focused on the Host and Task, so groups don’t really survive outside of inventory and host matching. By default, Ansible overwrites variables including the ones defined for a group and/or host (see the hash_merge setting to change this) . The order/precedence is (from lowest to highest):

all group (because it is the ‘parent’ of all other groups)

parent group

child group

host

When groups of the same parent/child level are merged, it is done alphabetically, and the last group loaded overwrites the previous groups. For example, an a_group will be merged with b_group and b_group vars that match will overwrite the ones in a_group.

New in version 2.4.

Starting in Ansible version 2.4, users can use the group variable ansible_group_priority to change the merge order for groups of the same level (after the parent/child order is resolved). The larger the number, the later it will be merged, giving it higher priority. This variable defaults to 1 if not set. For example:

a_group:testvar:aansible_group_priority:10b_group：testvar:b

In this example, if both groups have the same priority, the result would normally have been testvar==b, but since we are giving the a_group a higher priority the result will be testvar==a.

As described above, setting the following variables control how Ansible interacts with remote hosts.

Host connection:

Note

Ansible does not expose a channel to allow communication between the user and the ssh process to accept a password manually to decrypt an ssh key when using the ssh connection plugin (which is the default). The use of ssh-agent is highly recommended.

ansible_connection

Connection type to the host. This can be the name of any of ansible’s connection plugins. SSH protocol types are smart, ssh or paramiko. The default is smart. Non-SSH based types are described in the next section.

General for all connections:

ansible_host

The name of the host to connect to, if different from the alias you wish to give to it.

ansible_port

The ssh port number, if not 22

ansible_user

The default ssh user name to use.

Specific to the SSH connection:

ansible_ssh_pass

The ssh password to use (never store this variable in plain text; always use a vault. See Variables and Vaults)

ansible_ssh_private_key_file

Private key file used by ssh. Useful if using multiple keys and you don’t want to use SSH agent.

ansible_ssh_common_args

This setting is always appended to the default command line for sftp, scp,
and ssh. Useful to configure a ProxyCommand for a certain host (or
group).

ansible_sftp_extra_args

This setting is always appended to the default sftp command line.

ansible_scp_extra_args

This setting is always appended to the default scp command line.

ansible_ssh_extra_args

This setting is always appended to the default ssh command line.

ansible_ssh_pipelining

Determines whether or not to use SSH pipelining. This can override the pipelining setting in ansible.cfg.

ansible_ssh_executable (added in version 2.2)

This setting overrides the default behavior to use the system ssh. This can override the ssh_executable setting in ansible.cfg.

Equivalent to ansible_sudo or ansible_su, allows to force privilege escalation

ansible_become_method

Allows to set privilege escalation method

ansible_become_user

Equivalent to ansible_sudo_user or ansible_su_user, allows to set the user you become through privilege escalation

ansible_become_pass

Equivalent to ansible_sudo_pass or ansible_su_pass, allows you to set the privilege escalation password (never store this variable in plain text; always use a vault. See Variables and Vaults)

ansible_become_exe

Equivalent to ansible_sudo_exe or ansible_su_exe, allows you to set the executable for the escalation method selected

ansible_become_flags

Equivalent to ansible_sudo_flags or ansible_su_flags, allows you to set the flags passed to the selected escalation method. This can be also set globally in ansible.cfg in the sudo_flags option

Remote host environment parameters:

ansible_shell_type

The shell type of the target system. You should not use this setting unless you have set the
ansible_shell_executable to a non-Bourne (sh) compatible shell. By default commands are
formatted using sh-style syntax. Setting this to csh or fish will cause commands
executed on target systems to follow those shell’s syntax instead.

ansible_python_interpreter

The target host python path. This is useful for systems with more
than one Python or not located at /usr/bin/python such as *BSD, or where /usr/bin/python
is not a 2.X series Python. We do not use the /usr/bin/env mechanism as that requires the remote user’s
path to be set right and also assumes the python executable is named python, where the executable might
be named something like python2.6.

ansible_*_interpreter

Works for anything such as ruby or perl and works just like ansible_python_interpreter.
This replaces shebang of modules which will run on that host.

New in version 2.1.

ansible_shell_executable

This sets the shell the ansible controller will use on the target machine,
overrides executable in ansible.cfg which defaults to
/bin/sh. You should really only change it if is not possible
to use /bin/sh (i.e. /bin/sh is not installed on the target
machine or cannot be run from sudo.).

As stated in the previous section, Ansible executes playbooks over SSH but it is not limited to this connection type.
With the host specific parameter ansible_connection=<connector>, the connection type can be changed.
The following non-SSH based connectors are available:

local

This connector can be used to deploy the playbook to the control machine itself.

docker

This connector deploys the playbook directly into Docker containers using the local Docker client. The following parameters are processed by this connector:

ansible_host

The name of the Docker container to connect to.

ansible_user

The user name to operate within the container. The user must exist inside the container.

ansible_become

If set to true the become_user will be used to operate within the container.

ansible_docker_extra_args

Could be a string with any additional arguments understood by Docker, which are not command specific. This parameter is mainly used to configure a remote Docker daemon to use.

If you’re reading the docs from the beginning, this may be the first example you’ve seen of an Ansible playbook. This is not an inventory file.
Playbooks will be covered in great detail later in the docs.